summaryrefslogtreecommitdiffstats
path: root/crypto/asymmetric_keys/pkcs7_verify.c
blob: 44b746e9df1b4110e6f8da4ac5b23419cb63feac (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
/* Verify the signature on a PKCS#7 message.
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#define pr_fmt(fmt) "PKCS7: "fmt
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/asn1.h>
#include <crypto/hash.h>
#include <crypto/public_key.h>
#include "pkcs7_parser.h"

/*
 * Digest the relevant parts of the PKCS#7 data
 */
static int pkcs7_digest(struct pkcs7_message *pkcs7,
			struct pkcs7_signed_info *sinfo)
{
	struct public_key_signature *sig = sinfo->sig;
	struct crypto_shash *tfm;
	struct shash_desc *desc;
	size_t desc_size;
	int ret;

	kenter(",%u,%s", sinfo->index, sinfo->sig->hash_algo);

	if (!sinfo->sig->hash_algo)
		return -ENOPKG;

	/* Allocate the hashing algorithm we're going to need and find out how
	 * big the hash operational data will be.
	 */
	tfm = crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
	if (IS_ERR(tfm))
		return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : PTR_ERR(tfm);

	desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
	sig->digest_size = crypto_shash_digestsize(tfm);

	ret = -ENOMEM;
	sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
	if (!sig->digest)
		goto error_no_desc;

	desc = kzalloc(desc_size, GFP_KERNEL);
	if (!desc)
		goto error_no_desc;

	desc->tfm   = tfm;
	desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

	/* Digest the message [RFC2315 9.3] */
	ret = crypto_shash_init(desc);
	if (ret < 0)
		goto error;
	ret = crypto_shash_finup(desc, pkcs7->data, pkcs7->data_len,
				 sig->digest);
	if (ret < 0)
		goto error;
	pr_devel("MsgDigest = [%*ph]\n", 8, sig->digest);

	/* However, if there are authenticated attributes, there must be a
	 * message digest attribute amongst them which corresponds to the
	 * digest we just calculated.
	 */
	if (sinfo->authattrs) {
		u8 tag;

		if (!sinfo->msgdigest) {
			pr_warn("Sig %u: No messageDigest\n", sinfo->index);
			ret = -EKEYREJECTED;
			goto error;
		}

		if (sinfo->msgdigest_len != sig->digest_size) {
			pr_debug("Sig %u: Invalid digest size (%u)\n",
				 sinfo->index, sinfo->msgdigest_len);
			ret = -EBADMSG;
			goto error;
		}

		if (memcmp(sig->digest, sinfo->msgdigest,
			   sinfo->msgdigest_len) != 0) {
			pr_debug("Sig %u: Message digest doesn't match\n",
				 sinfo->index);
			ret = -EKEYREJECTED;
			goto error;
		}

		/* We then calculate anew, using the authenticated attributes
		 * as the contents of the digest instead.  Note that we need to
		 * convert the attributes from a CONT.0 into a SET before we
		 * hash it.
		 */
		memset(sig->digest, 0, sig->digest_size);

		ret = crypto_shash_init(desc);
		if (ret < 0)
			goto error;
		tag = ASN1_CONS_BIT | ASN1_SET;
		ret = crypto_shash_update(desc, &tag, 1);
		if (ret < 0)
			goto error;
		ret = crypto_shash_finup(desc, sinfo->authattrs,
					 sinfo->authattrs_len, sig->digest);
		if (ret < 0)
			goto error;
		pr_devel("AADigest = [%*ph]\n", 8, sig->digest);
	}

error:
	kfree(desc);
error_no_desc:
	crypto_free_shash(tfm);
	kleave(" = %d", ret);
	return ret;
}

/*
 * Find the key (X.509 certificate) to use to verify a PKCS#7 message.  PKCS#7
 * uses the issuer's name and the issuing certificate serial number for
 * matching purposes.  These must match the certificate issuer's name (not
 * subject's name) and the certificate serial number [RFC 2315 6.7].
 */
static int pkcs7_find_key(struct pkcs7_message *pkcs7,
			  struct pkcs7_signed_info *sinfo)
{
	struct x509_certificate *x509;
	unsigned certix = 1;

	kenter("%u", sinfo->index);

	for (x509 = pkcs7->certs; x509; x509 = x509->next, certix++) {
		/* I'm _assuming_ that the generator of the PKCS#7 message will
		 * encode the fields from the X.509 cert in the same way in the
		 * PKCS#7 message - but I can't be 100% sure of that.  It's
		 * possible this will need element-by-element comparison.
		 */
		if (!asymmetric_key_id_same(x509->id, sinfo->sig->auth_ids[0]))
			continue;
		pr_devel("Sig %u: Found cert serial match X.509[%u]\n",
			 sinfo->index, certix);

		if (x509->pub->pkey_algo != sinfo->sig->pkey_algo) {
			pr_warn("Sig %u: X.509 algo and PKCS#7 sig algo don't match\n",
				sinfo->index);
			continue;
		}

		sinfo->signer = x509;
		return 0;
	}

	/* The relevant X.509 cert isn't found here, but it might be found in
	 * the trust keyring.
	 */
	pr_debug("Sig %u: Issuing X.509 cert not found (#%*phN)\n",
		 sinfo->index,
		 sinfo->sig->auth_ids[0]->len, sinfo->sig->auth_ids[0]->data);
	return 0;
}

/*
 * Verify the internal certificate chain as best we can.
 */
static int pkcs7_verify_sig_chain(struct pkcs7_message *pkcs7,
				  struct pkcs7_signed_info *sinfo)
{
	struct public_key_signature *sig;
	struct x509_certificate *x509 = sinfo->signer, *p;
	struct asymmetric_key_id *auth;
	int ret;

	kenter("");

	for (p = pkcs7->certs; p; p = p->next)
		p->seen = false;

	for (;;) {
		pr_debug("verify %s: %*phN\n",
			 x509->subject,
			 x509->raw_serial_size, x509->raw_serial);
		x509->seen = true;
		if (x509->unsupported_key)
			goto unsupported_crypto_in_x509;

		pr_debug("- issuer %s\n", x509->issuer);
		sig = x509->sig;
		if (sig->auth_ids[0])
			pr_debug("- authkeyid.id %*phN\n",
				 sig->auth_ids[0]->len, sig->auth_ids[0]->data);
		if (sig->auth_ids[1])
			pr_debug("- authkeyid.skid %*phN\n",
				 sig->auth_ids[1]->len, sig->auth_ids[1]->data);

		if (x509->self_signed) {
			/* If there's no authority certificate specified, then
			 * the certificate must be self-signed and is the root
			 * of the chain.  Likewise if the cert is its own
			 * authority.
			 */
			if (x509->unsupported_sig)
				goto unsupported_crypto_in_x509;
			x509->signer = x509;
			pr_debug("- self-signed\n");
			return 0;
		}

		/* Look through the X.509 certificates in the PKCS#7 message's
		 * list to see if the next one is there.
		 */
		auth = sig->auth_ids[0];
		if (auth) {
			pr_debug("- want %*phN\n", auth->len, auth->data);
			for (p = pkcs7->certs; p; p = p->next) {
				pr_debug("- cmp [%u] %*phN\n",
					 p->index, p->id->len, p->id->data);
				if (asymmetric_key_id_same(p->id, auth))
					goto found_issuer_check_skid;
			}
		} else {
			auth = sig->auth_ids[1];
			pr_debug("- want %*phN\n", auth->len, auth->data);
			for (p = pkcs7->certs; p; p = p->next) {
				if (!p->skid)
					continue;
				pr_debug("- cmp [%u] %*phN\n",
					 p->index, p->skid->len, p->skid->data);
				if (asymmetric_key_id_same(p->skid, auth))
					goto found_issuer;
			}
		}

		/* We didn't find the root of this chain */
		pr_debug("- top\n");
		return 0;

	found_issuer_check_skid:
		/* We matched issuer + serialNumber, but if there's an
		 * authKeyId.keyId, that must match the CA subjKeyId also.
		 */
		if (sig->auth_ids[1] &&
		    !asymmetric_key_id_same(p->skid, sig->auth_ids[1])) {
			pr_warn("Sig %u: X.509 chain contains auth-skid nonmatch (%u->%u)\n",
				sinfo->index, x509->index, p->index);
			return -EKEYREJECTED;
		}
	found_issuer:
		pr_debug("- subject %s\n", p->subject);
		if (p->seen) {
			pr_warn("Sig %u: X.509 chain contains loop\n",
				sinfo->index);
			return 0;
		}
		ret = public_key_verify_signature(p->pub, p->sig);
		if (ret < 0)
			return ret;
		x509->signer = p;
		if (x509 == p) {
			pr_debug("- self-signed\n");
			return 0;
		}
		x509 = p;
		might_sleep();
	}

unsupported_crypto_in_x509:
	/* Just prune the certificate chain at this point if we lack some
	 * crypto module to go further.  Note, however, we don't want to set
	 * sinfo->unsupported_crypto as the signed info block may still be
	 * validatable against an X.509 cert lower in the chain that we have a
	 * trusted copy of.
	 */
	return 0;
}

/*
 * Verify one signed information block from a PKCS#7 message.
 */
static int pkcs7_verify_one(struct pkcs7_message *pkcs7,
			    struct pkcs7_signed_info *sinfo)
{
	int ret;

	kenter(",%u", sinfo->index);

	/* First of all, digest the data in the PKCS#7 message and the
	 * signed information block
	 */
	ret = pkcs7_digest(pkcs7, sinfo);
	if (ret < 0)
		return ret;

	/* Find the key for the signature if there is one */
	ret = pkcs7_find_key(pkcs7, sinfo);
	if (ret < 0)
		return ret;

	if (!sinfo->signer)
		return 0;

	pr_devel("Using X.509[%u] for sig %u\n",
		 sinfo->signer->index, sinfo->index);

	/* Check that the PKCS#7 signing time is valid according to the X.509
	 * certificate.  We can't, however, check against the system clock
	 * since that may not have been set yet and may be wrong.
	 */
	if (test_bit(sinfo_has_signing_time, &sinfo->aa_set)) {
		if (sinfo->signing_time < sinfo->signer->valid_from ||
		    sinfo->signing_time > sinfo->signer->valid_to) {
			pr_warn("Message signed outside of X.509 validity window\n");
			return -EKEYREJECTED;
		}
	}

	/* Verify the PKCS#7 binary against the key */
	ret = public_key_verify_signature(sinfo->signer->pub, sinfo->sig);
	if (ret < 0)
		return ret;

	pr_devel("Verified signature %u\n", sinfo->index);

	/* Verify the internal certificate chain */
	return pkcs7_verify_sig_chain(pkcs7, sinfo);
}

/**
 * pkcs7_verify - Verify a PKCS#7 message
 * @pkcs7: The PKCS#7 message to be verified
 * @usage: The use to which the key is being put
 *
 * Verify a PKCS#7 message is internally consistent - that is, the data digest
 * matches the digest in the AuthAttrs and any signature in the message or one
 * of the X.509 certificates it carries that matches another X.509 cert in the
 * message can be verified.
 *
 * This does not look to match the contents of the PKCS#7 message against any
 * external public keys.
 *
 * Returns, in order of descending priority:
 *
 *  (*) -EKEYREJECTED if a key was selected that had a usage restriction at
 *      odds with the specified usage, or:
 *
 *  (*) -EKEYREJECTED if a signature failed to match for which we found an
 *	appropriate X.509 certificate, or:
 *
 *  (*) -EBADMSG if some part of the message was invalid, or:
 *
 *  (*) -ENOPKG if none of the signature chains are verifiable because suitable
 *	crypto modules couldn't be found, or:
 *
 *  (*) 0 if all the signature chains that don't incur -ENOPKG can be verified
 *	(note that a signature chain may be of zero length), or:
 */
int pkcs7_verify(struct pkcs7_message *pkcs7,
		 enum key_being_used_for usage)
{
	struct pkcs7_signed_info *sinfo;
	int enopkg = -ENOPKG;
	int ret;

	kenter("");

	switch (usage) {
	case VERIFYING_MODULE_SIGNATURE:
		if (pkcs7->data_type != OID_data) {
			pr_warn("Invalid module sig (not pkcs7-data)\n");
			return -EKEYREJECTED;
		}
		if (pkcs7->have_authattrs) {
			pr_warn("Invalid module sig (has authattrs)\n");
			return -EKEYREJECTED;
		}
		break;
	case VERIFYING_FIRMWARE_SIGNATURE:
		if (pkcs7->data_type != OID_data) {
			pr_warn("Invalid firmware sig (not pkcs7-data)\n");
			return -EKEYREJECTED;
		}
		if (!pkcs7->have_authattrs) {
			pr_warn("Invalid firmware sig (missing authattrs)\n");
			return -EKEYREJECTED;
		}
		break;
	case VERIFYING_KEXEC_PE_SIGNATURE:
		if (pkcs7->data_type != OID_msIndirectData) {
			pr_warn("Invalid kexec sig (not Authenticode)\n");
			return -EKEYREJECTED;
		}
		/* Authattr presence checked in parser */
		break;
	case VERIFYING_UNSPECIFIED_SIGNATURE:
		if (pkcs7->data_type != OID_data) {
			pr_warn("Invalid unspecified sig (not pkcs7-data)\n");
			return -EKEYREJECTED;
		}
		break;
	default:
		return -EINVAL;
	}

	for (sinfo = pkcs7->signed_infos; sinfo; sinfo = sinfo->next) {
		ret = pkcs7_verify_one(pkcs7, sinfo);
		if (ret < 0) {
			if (ret == -ENOPKG) {
				sinfo->unsupported_crypto = true;
				continue;
			}
			kleave(" = %d", ret);
			return ret;
		}
		enopkg = 0;
	}

	kleave(" = %d", enopkg);
	return enopkg;
}
EXPORT_SYMBOL_GPL(pkcs7_verify);

/**
 * pkcs7_supply_detached_data - Supply the data needed to verify a PKCS#7 message
 * @pkcs7: The PKCS#7 message
 * @data: The data to be verified
 * @datalen: The amount of data
 *
 * Supply the detached data needed to verify a PKCS#7 message.  Note that no
 * attempt to retain/pin the data is made.  That is left to the caller.  The
 * data will not be modified by pkcs7_verify() and will not be freed when the
 * PKCS#7 message is freed.
 *
 * Returns -EINVAL if data is already supplied in the message, 0 otherwise.
 */
int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
			       const void *data, size_t datalen)
{
	if (pkcs7->data) {
		pr_debug("Data already supplied\n");
		return -EINVAL;
	}
	pkcs7->data = data;
	pkcs7->data_len = datalen;
	return 0;
}